Implantable medical devices (IMDs) can perform a variety of diagnostic or therapeutic functions. In an example, an IMD can include one or more cardiac function management features, such as to monitor the heart or to provide electrical stimulation to a heart or to the nervous system, such as to diagnose or treat a subject, such as one or more electrical or mechanical abnormalities of the heart. Examples of IMDs can include pacers, automatic implantable cardioverter-defibrillators (ICDs), cardiac resynchronization therapy (CRT) devices, implantable monitors, neuromodulation devices (e.g., deep brain stimulators, or other neural stimulators), cochlear implants, or drug pumps, among others.
Nuclear magnetic resonance imaging (MRI) is a medical imaging technique that can be used to visualize internal structure of the body. MRI is an increasingly common diagnostic tool, but can pose risks to a person with an IMD, such as a patient undergoing an MRI scan or a person nearby MRI equipment, or to people having a conductive implant.
In an MR field, an item, such as an IMD, can be referred to as “MR Safe” if the item poses no known hazard in all MRI environments. In an example, MR Safe items can include non-conducting, non-metallic, non-magnetic materials, such as glass, porcelain, a non-conductive polymer, etc. An item can be referred to as “MR Conditional” in the MR field if the item has been demonstrated to pose no known hazards in a specified MRI environment with specified conditions of use (e.g., static magnetic field strength, spatial gradient, time-varying magnetic fields, RF fields, etc.). In certain examples, MR Conditional items can be labeled with testing results sufficient to characterize item behavior in a specified MRI environment. Testing can include, among other things, magnetically induced displacement or torque, heating, induced current or voltage, or one or more other factors. An item known to pose hazards in all MRI environments, such as a ferromagnetic scissors, can be referred to as “MR Unsafe.”